Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $45.38   11.561%   $50.6264   $50.63   $50.65   $50.60  
  Purchase #2 $226.71   10.351%   $250.1768   $250.18   $250.20   $250.20  
  Purchase #3 $127.42   3.803%   $132.2658   $132.27   $132.25   $132.30  
  Purchase #4 $127.26   4.512%   $133.002   $133.00   $133.00   $133.00  
  Purchase #5 $62.88   11.609%   $70.1797   $70.18   $70.20   $70.20  
  Purchase #6 $51.76   6.123%   $54.9293   $54.93   $54.95   $54.90  
  Purchase #7 $153.53   10.321%   $169.3758   $169.38   $169.40   $169.40  
  7 purchase totals = $794.94       $860.5558   $860.57   $860.65   $860.60